Conventionally known and industrially applicable is a method for winding a false twisted yarn in a false twisting texturing machine wherein the false twisted yarn delivered from a delivery roller is generally wound on a bobbin after it passes by a guide fixedly secured at a position of the fulcrum for traverse motion of a winding apparatus or after it passes by a bar guide disposed between the delivery roller and the winding apparatus along the axis of the bobbin and having an engaging surface over which the yarn wraps around and over which the yarn slides along the lengthwise direction. According to such a conventional method, the above-mentioned fixed guide and bar guide may be harmful to a stable soft winding of the false twisted yarn into a cheese. More specifically, when the false twisted yarn is wound into a cheese, especially a soft cheese having an apparent density of equal to or less than 0.3 g/cm.sup.3, the yarn may be slacked because of the friction with the fixed or bar guide, and accordingly tension fluctuation in the yarn may occur. As a result, it becomes very difficult to stably wind a false twisted yarn, and the apparent density of the thus obtained cheese is not uniform, and furthermore the shape of the obtained cheese becomes bad. In addition, it should be noted that the differences in the size and the surface condition of the fixed or bar guide affect the influence regarding the apparent density and the wound shape of the cheese, and therefore the changes in the size and the surface condition of the fixed or bar guide as the operating time period lapses affects a serious influence to the apparent density and the wound shape of the cheese.
The inventors of the present invention effected various surveys concerning the causes of the defects, i.e., the non-uniformity of the apparent density of a cheese and the undesirable shape of the cheese. As a result, they found that the defects appear more often as the yarn winding speed, the winding feed ratio or the time period which it takes for the false twisted yarn to travel from the yarn delivery means disposed nearest the winding apparatus to the bobbin rotatably supported in the winding apparatus is increased. However, in a conventional winding method, any attempt to obviate such defects has not been carried out because the results obtained by the inventors' surveys have not been understood completely.
In addition, a conventional soft wound cheese which is wound on a bobbin successively after the false twisting operation in a false twisting texturing machine has a disadvantage. The disadvantage is in that, when the obtained soft wound cheese is subjected to a conventionally known steam set or dyeing operation while it is in a soft wound cheese and then it is rewound to form a cone of a heat treated or dyed yarn, the heat treated or dyed yarn thus obtained suffers from uneveness in crimp characteristics and dyeability in accordance with the locations of the yarn in the cheese. The uneveness can be observed, for example, between the yarns at the innermost portion, intermediate portion or the outermost portion with respect to the radial direction of the cheese, or between the yarns at the end portion or the central portion with respect to the axial direction of the cheese. The main cause of the disadvantage exists in the fact that the apparent density in a soft wound cheese obtained according to a conventionally known method varies in accordance to the location in the cheese. Another cause of the disadvantage is in the fact that the apparent density in a soft wound cheese is not entirely uniform but varies locally. Such a variation in apparent density is caused by the changes in winding conditions, such as the tension in the yarn, which causes the bulges on the lateral end surface of the cheese. In other words, a soft wound cheese with a bad shape, i.e., a bulged cheese, does not have a uniform apparent density, and therefore, it has a tendency that the heat treated or dyed yarn obtained therefrom in accordance with package steam setting or dyeing may suffer from the deterioration of its crimp characteristics and dyeability.
Also considered to be a cause of the above-mentioned disadvantage is the non-uniformity of the shrinkage of the false twisted yarn which is subjected to a heat treatment as a soft wound cheese. More specifically, the yarn at the innermost portion in the cheese is not permitted to shrink freely because its shrinkage is suppressed by the bobbin, and in addition it is elongated because it receives a compressive force caused by the shrinking force of the yarn located around the outermost portion. On the other hand, the yarn located at the outermost portion in the cheese slightly slacks. As a result, differences in the heat shrinkage and the apparent density between the locations are created, and the above-mentioned disadvantage occurs.
U.S. Pat. No. 3,987,611 discloses a method for winding a textured yarn, wherein a specially designed complicated speed converter for controlling a winding feed is applied in order to obtain a yarn with uniform stretch properties. However, since such a converter is complicated, a method which utilizes a simple device and by which a yarn is effectively soft wound has been desired.